1. Field of the Invention
The present invention relates to antenna reflectors, and, more particularly, heated antenna reflectors.
2. Description of the Related Art
A reflector, commonly called a dish, is generally a parabolic section having a round, elliptical or other configuration. A reflector functions to gather radio or microwave frequency energy transmitted from the feedhorn or through the ambient environment from an external transmitter. The reflector can thus be used to receive and transmit signals to and from the satellite system. Most satellites are in equatorial orbit. Thus, it is necessary to adjust the direction angle at which the reflector faces, depending upon the latitude of the earth station location. At least some of the support structure of the reflector, such as a support arm which supports the feedhorn, is rigidly attached to the reflector such that the angle between the support arm and the horizon also varies with the latitude of the earth station location.
Reflectors are usually located outdoors, where snow and ice may collect on the receiving or concave side, degrading the performance of the reflector. To prevent such accumulation of ice and snow on the reflecting surface, electrical heaters are used to heat at least the lower part of the reflecting surface. In order to minimize the power used to keep the reflecting surface clear of ice and snow, a control device can be used to activate the heater only when it is needed. The control device can include a temperature sensor and a moisture sensor which together sense the presence of frozen precipitation and send a signal to an electrical processor to activate the heater.
The moisture sensor is typically attached to the support arm of the reflector. This mounting location has the advantage of being in close proximity to the reflecting surface in order to accurately sense the environmental conditions to which the reflecting surface is exposed. Also, the moisture sensor, when mounted to the support arm, is not excessively shielded by the reflector. A problem with mounting the moisture sensor on the support arm is that the sensing grid of the moisture sensor must be kept substantially horizontal in order to most effectively sense the presence of snow. However, as described above, the angular orientation of the support arm is variable. Thus, the variable angular orientation of the support arm creates difficulties in mounting the moisture sensor such that the sensor grid is kept horizontal.
Another problem is that the decision to install a heater and its associated sensors must be made before manufacture of the reflector. Often this decision must be made before knowing the latitudinal position at which the reflector will be located.
What is needed in the art is a sensor assembly which can be installed on the support arm of a heated antenna reflector such that the presence of snow can be effectively sensed, regardless of the angular orientation of the support arm.